That is pretty crazy how lean they can run. I havn't been able to spot very good sources to compair parts side by side, the only reasion the head is a must is because the injectors are mounted in the head instead of the intake tubes. I read a post that the pistons might be different, but no photos or any kind of confirmed details. I beleive the compression ratio is the same in both engines (9.5:1), just not sure if the head/pistons have a different design for the lean burn.
I read in other areas that lean burn takes out the cat over time. That could be a problem as well since I read mine has 2 cats, I have only noticed one though while not really looking for them.
It would be really neat if all I had to do is get the head (for the closer injectors / head design), ecu, and the wide band o2 sensor to make this work, but I have a feeling it is more complicated than that.
For cost effectiveness of the mod, if I go to rebuild the engine, the extra parts wouldn't be much more. Of course buying a low miles engine would probably be the cheapest way out, and cheap is good
.